Method to package multiple MEMS sensors and actuators at different gases and cavity pressures

ABSTRACT

A semiconductor device having multiple MEMS (micro-electro mechanical system) devices includes a semiconductor substrate having a first MEMS device and a second MEMS device, and an encapsulation substrate having a top portion and sidewalls forming a first cavity and a second cavity. The encapsulation substrate is bonded to the semiconductor substrate at the sidewalls to encapsulate the first MEMS device in the first cavity and to encapsulate the second MEMS device in the second cavity. The second cavity includes at least one access channel at a recessed region in a sidewall of the encapsulation substrate adjacent to an interface between the encapsulation substrate and the semiconductor substrate. The access channel is covered by a thin film. The first cavity is at a first atmospheric pressure and the second cavity is at a second atmospheric pressure. The second air pressure is different from the first air pressure.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation patent application of U.S.patent application Ser. No. 14/102,465, filed Dec. 10, 2013, whichclaims priority to U.S. Pat. App. No. 61/735,553, filed Dec. 10, 2012,both of which are incorporated by reference in their entirety herein forall purposes. This application is also related to concurrently filedU.S. patent application Ser. No. 14/887,622, titled “METHOD TO PACKAGEMULTIPLE MEMS SENSORS AND ACTUATORS AT DIFFERENT GASES AND CAVITYPRESSURES,” whose content is incorporated by reference in their entiretyherein for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to integrated electronic devicesand systems. In particular, the present invention provides a method forpackaging multiple micro-electro mechanical systems (MEMS) sensors andactuators. Merely by way of example, the MEMS devices can include anaccelerometer, a gyroscope, a magnetic sensor, a pressure sensor, amicrophone, a humidity sensor, a temperature sensor, a chemical sensor,a biosensor, an inertial sensor, and others. But it will be recognizedthat the invention has a much broader range of applicability.

Research and development in integrated microelectronics have continuedto produce astounding progress in CMOS, magnetic field sensors, andMEMS. CMOS technology has become the predominant fabrication technologyfor integrated circuits (IC). In layman's terms, microelectronic ICs arethe “brains” of an integrated device which provides decision-makingcapabilities, whereas MEMS, magnetic field sensors, and others, are the“eyes” and “arms” that provide the ability to sense and control theenvironment. Some examples of the widespread application of thesetechnologies are the switches in radio frequency (RF) antenna systems,such as those in the iPhone™ device by Apple, Inc. of Cupertino, Calif.,and the Blackberry™ phone by Research In Motion Limited of Waterloo,Ontario, Canada, and accelerometers in sensor-equipped game devices,such as those in the Wii™ controller manufactured by Nintendo CompanyLimited of Japan. Though they are not always easily identifiable, thesetechnologies are becoming ever more prevalent in society every day.

Beyond consumer electronics, use of IC, magnetic field sensing, and MEMStechnology has limitless applications through modular measurementdevices such as accelerometers, angular rate sensors, transducers,actuators, and other sensors and devices. In conventional vehicles,accelerometers and angular rate sensors are used to deploy airbags andtrigger dynamic stability control functions, respectively. Magneticsensors are commonly used in compass systems, such as those used inaircrafts to determine heading, pitch and roll. MEMS gyroscopes can alsobe used for image stabilization systems in video and still cameras, andautomatic steering systems in airplanes and torpedoes. Biological MEMS(Bio-MEMS) implement biosensors and chemical sensors for Lab-On-Chipapplications, which integrate one or more laboratory functions on asingle millimeter-sized chip only. Other applications include Internetand telephone networks, security and financial applications, health careand medical systems and the like. Magnetic sensors have also been usedin applications requiring proximity switching, positioning, speeddetection, current sensing and the like. As described previously, ICs,magnetic field sensors, and MEMS can be used to practically engage invarious type of environmental interaction.

Although highly successful, ICs and in particular magnetic field sensorsand MEMS still have limitations. Similar to IC development, magneticsensor and MEMS development, which focuses on increasing performance,reducing size, and decreasing cost, continues to be challenging.Additionally, applications of magnetic sensors and MEMS often requireincreasingly complex microsystems that desire greater computationalpower. Unfortunately, such applications generally do not exist. Theseand other limitations of conventional magnetic sensors, MEMS, and ICsmay be further described throughout the present specification and moreparticularly below.

From the above, it is seen that techniques for improving operation ofintegrated circuit devices, magnetic field sensors, and MEMS are highlydesired.

BRIEF SUMMARY OF THE INVENTION

According to embodiments of the present invention, techniques generallyrelated to integrated electronic devices and systems are provided. Inparticular, the present invention provides a method for packagingmultiple MEMS sensors and actuators. Merely by way of example, the MEMSdevices can include an accelerometer, a gyroscope, a magnetic sensor, apressure sensor, a microphone, a humidity sensor, a temperature sensor,a chemical sensor, a biosensor, an inertial sensor, and others. But itwill be recognized that the invention has a much broader range ofapplicability.

The performance of MEMS devices have been found to be highly dependenton their operation pressures. Different MEMS devices can have optimaloperating pressures. For example, MEMS accelerometers may require ahigher operating pressure to ensure their performance and reliability.At low pressures, a MEMS accelerometer could have non-ideal oscillations(“ringing”) under a sudden change of input acceleration, which makes theoutput signal of the accelerometer unstable. This non-ideal oscillationcan be suppressed by increasing the air pressure of the environmentaround the accelerometer with a sealing gas, which can increase thedamping of the accelerometer. High cavity pressure can also help toreduce the impact force due to the collision of the accelerometer'sproof mass with the motion stoppers by acting as a damper and reducingthe collision velocity.

On the other hand, resonance based sensors, such as gyroscopes andmagnetometers, may require low operating pressures to minimize thedamping during their operations. These sensors have larger sensitivitiesand lower power consumption at lower operation pressures. Similarly,MEMS resonators, which are used for oscillators and filters, may requirelow pressure to minimize damping as well or to maximize their qualityfactors. MEMS oscillators for timing reference applications need highquality factors to reduce the impact of close-to-carrier phase noise.MEMS filters may also require high quality factors for high frequencysensitivity. MEMS based infrared sensors, such as micro-bolometers mayalso require low operating pressures to minimize the thermal conductionthrough the surrounding gas and to maximize their sensitivity.

Wafer-level packaging techniques have often been used to control andmaintain the operating conditions of MEMS devices. Various embodimentsof the present invention include using a silicon wafer with cavities asan encapsulation layer, which is bonded overlying a wafer withfabricated MEMS devices, sealing the cavities. The bonding methods caninclude eutectic bonding, glass-fit seal, and fusion bonding. Thepressure within the cavities (operational pressure) is defined by thepressure during the sealing process. However, conventional wafer-levelpackaging processes only provide a single operating pressure across awafer.

It is an object of the present invention to develop methods offabricating integrated electronic devices that include different MEMSdevices on one silicon chip or wafer. Integrating multiple MEMS deviceson a single chip or wafer can reduce the die size and manufacturingcosts. One of the difficulties of integrating different MEMS devices isthe varying requirements of operational pressures, since conventionalpackaging methods cannot vary the sealing pressure from device todevice. As seen from the above, it is an object of the present inventionto develop a wafer-level packaging method that allows different devices,such as MEMS devices, to be sealed within different operation pressureson the same wafer or die.

In an embodiment, present invention includes a method for fabricating amultiple MEMS device including providing a semiconductor substratehaving a first and second MEMS device, and an encapsulation wafer with afirst cavity and a second cavity, which includes at least one channel.In a specific embodiment, the first MEMS device can be selected from amagnetometer, a gyroscope, accelerometer, an oscillator, a filter, aninfrared sensor, and the like. The channel of the second cavity can havea depth that is less than the depth of the first and second cavities.

The first MEMS can be encapsulated within the first cavity and thesecond MEMS device can be encapsulated within the second cavity. Thesedevices can be encapsulated within a provided first encapsulationenvironment at a first air pressure, encapsulating the first MEMS devicewithin the first cavity at the first air pressure. In a specificembodiment, the first air pressure can be below atmospheric pressure orabove atmospheric pressure. The first encapsulation environment caninclude gases such as helium, xenon, krypton, argon, and the like.

The second MEMS device within the second cavity can then be subjected toa provided second encapsulating environment at a second air pressure viathe channel of the second cavity. In a specific embodiment, the firstair pressure can be below the second air pressure. The channel can besealed while within the second encapsulation environment, encapsulatingthe second MEMS device within the second cavity at the second airpressure. In a specific embodiment, the sealing of the channel caninclude depositing a layer of material using chemical vapor deposition(CVD), plasma vapor deposition (PVD), sputtering, evaporation, and thelike.

In a specific embodiment, the present method can further includeproviding an initial encapsulation wafer and patterning a masking layeron top of the initial encapsulation wafer. The masking layer can includea first, second, and third opening. The width of the third opening canbe substantially smaller than a width of either the first or secondopening. The initial encapsulation wafer can be etched to form theencapsulation layer with the first cavity, second cavity, and channelbeing associated with the first opening, second opening, and thirdopening, respectively. Those of ordinary skills in the art willrecognize other variations, modifications, and alternatives.

Many benefits are achieved by way of embodiments the present inventionover conventional techniques. For example, embodiments of the presenttechnique provide an easy to use process to integrate a multipledifferent MEMS devices on a single die. In some embodiments, the methodprovides higher device yields in dies per wafer with the integratedapproach. Additionally, the method provides a process and system thatare compatible with conventional semiconductor and MEMS processtechnologies without substantial modifications to conventional equipmentand processes. Preferably, the invention provides for an improvedmulti-MEMS systems and related applications for a variety of uses.Depending upon the embodiment, one or more of these benefits may beachieved. These and other benefits will be described in more throughoutthe present specification and more particularly below.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

These diagrams are merely an example, which should not unduly limit thescope of the claims herein. One of ordinary skill in the art wouldrecognize many other variations, modifications, and alternatives. It isalso understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this process and scopeof the appended claims.

FIG. 1 illustrates a simplified cross-sectional diagram of a method stepof providing a semiconductor substrate with MEMS devices according to anembodiment of the present invention;

FIG. 2A illustrates a simplified top view diagram of a method step ofproviding an encapsulation wafer with cavities according to anembodiment of the present invention;

FIG. 2B illustrates a simplified cross-sectional diagram of a methodstep of providing an encapsulation wafer with cavities according to anembodiment of the present invention;

FIG. 3 illustrates a simplified cross-sectional diagram of a method stepof encapsulating the MEMS devices within cavities according to anembodiment of the present invention;

FIG. 4 illustrates a simplified cross-sectional diagram of a method stepof etching the cap wafer to vent a cavity according to an embodiment ofthe present invention;

FIG. 5 illustrates a simplified cross-sectional diagram of a method stepof depositing a thin film to seal a cavity according to an embodiment ofthe present invention;

FIG. 6 illustrates a simplified cross-sectional diagram of a method stepof opening bond pads according to an embodiment of the presentinvention;

FIG. 7 illustrates a simplified cross-sectional diagram of a method stepof providing a semiconductor substrate with MEMS devices according to anembodiment of the present invention;

FIG. 8A illustrates a simplified top view diagram of a method step ofproviding an encapsulation wafer with cavities according to anembodiment of the present invention;

FIG. 8B illustrates a simplified cross-sectional diagram of a methodstep of providing an encapsulation wafer with cavities according to anembodiment of the present invention;

FIG. 9 illustrates a simplified cross-sectional diagram of a method stepof encapsulating the MEMS devices within cavities by bonding the wafercap to the device layer according to an embodiment of the presentinvention;

FIG. 10 illustrates a simplified cross-sectional diagram of a methodstep of etching the cap wafer to vent a cavity according to anembodiment of the present invention;

FIG. 11 illustrates a simplified cross-sectional diagram of a methodstep of depositing a thin film to seal a cavity according to anembodiment of the present invention;

FIG. 12 illustrates a simplified cross-sectional diagram of a methodstep of creating a vent hole in the device layer according to anembodiment of the present invention; and

FIG. 13 illustrates a simplified cross-sectional diagram of a methodstep of creating a vent hole in the dielectric or interconnect layeraccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, techniques generallyrelated to integrated electronic devices and systems are provided. Inparticular, the present invention provides a method for packagingmultiple MEMS sensors and actuators. Merely by way of example, the MEMSdevices can include an accelerometer, a gyroscope, a magnetic sensor, apressure sensor, a microphone, a humidity sensor, a temperature sensor,a chemical sensor, a biosensor, an inertial sensor, and others. But itwill be recognized that the invention has a much broader range ofapplicability.

The performance of MEMS devices have been found to be highly dependenton their operation pressures. Different MEMS devices can have optimaloperating pressures. For example, MEMS accelerometers may require ahigher operating pressure to ensure their performance and reliability.At low pressures, a MEMS accelerometer could have non-ideal oscillations(“ringing”) under a sudden change of input acceleration, which makes theoutput signal of the accelerometer unstable. This non-ideal oscillationcan be suppressed by increasing the air pressure of the environmentaround the accelerometer with a sealing gas, which can increase thedamping of the accelerometer. High cavity pressure can also help toreduce the impact force due to the collision of the accelerometer'sproof mass with the motion stoppers by acting as a damper and reducingthe collision velocity.

On the other hand, resonance based sensors, such as gyroscopes andmagnetometers, may require low operating pressures to minimize thedamping during their operations. These sensors have larger sensitivitiesand lower power consumption at lower operation pressures. Similarly,MEMS resonators, which are used for oscillators and filters, may requirelow pressure to minimize damping as well or to maximize their qualityfactors. MEMS oscillators for timing reference applications need highquality factors to reduce the impact of close-to-carrier phase noise.MEMS filters may also require high quality factors for high frequencysensitivity. MEMS based infrared sensors, such as micro-bolometers mayalso require low operating pressures to minimize the thermal conductionthrough the surrounding gas and to maximize their sensitivity.

Wafer-level packaging techniques have often been used to control andmaintain the operating conditions of MEMS devices. Various embodimentsof the present invention include using a silicon wafer with cavities asan encapsulation layer, which is bonded overlying a wafer withfabricated MEMS devices, sealing the cavities. The bonding methods caninclude eutectic bonding, glass-fit seal, and fusion bonding. Thepressure within the cavities (operational pressure) is defined by thepressure during the sealing process. However, conventional wafer-levelpackaging processes only provide a single operating pressure across awafer.

It is an object of the present invention to develop methods offabricating integrated electronic devices that include different MEMSdevices on one silicon chip or wafer. Integrating multiple MEMS deviceson a single chip or wafer can reduce the die size and manufacturingcosts. One of the difficulties of integrating different MEMS devices isthe varying requirements of operational pressures, since conventionalpackaging methods cannot vary the sealing pressure from device todevice. As seen from the above, it is an object of the present inventionto develop a wafer-level packaging method that allows different devices,such as MEMS devices, to be sealed within different operation pressureson the same wafer or die.

In an embodiment, present invention includes a method for fabricating amultiple MEMS device including providing a semiconductor substratehaving a first and second MEMS device, and an encapsulation wafer with afirst cavity and a second cavity, which includes at least one channel.In a specific embodiment, the first MEMS device can be selected from amagnetometer, a gyroscope, accelerometer, an oscillator, a filter, aninfrared sensor, and the like. The channel of the second cavity can havea depth that is less than the depth of the first and second cavities.

The first MEMS can be encapsulated within the first cavity and thesecond MEMS device can be encapsulated within the second cavity. Thesedevices can be encapsulated within a provided first encapsulationenvironment at a first air pressure, encapsulating the first MEMS devicewithin the first cavity at the first air pressure. In a specificembodiment, the first air pressure can be below atmospheric pressure orabove atmospheric pressure. The first encapsulation environment caninclude gases such as helium, xenon, krypton, argon, and the like.

The second MEMS device within the second cavity can then be subjected toa provided second encapsulating environment at a second air pressure viathe channel of the second cavity. In a specific embodiment, the firstair pressure can be below the second air pressure. The channel can besealed while within the second encapsulation environment, encapsulatingthe second MEMS device within the second cavity at the second airpressure. In a specific embodiment, the sealing of the channel caninclude depositing a layer of material using chemical vapor deposition(CVD), plasma vapor deposition (PVD), sputtering, evaporation, and thelike.

In a specific embodiment, the present method can further includeproviding an initial encapsulation wafer and patterning a masking layeron top of the initial encapsulation wafer. The masking layer can includea first, second, and third opening. The width of the third opening canbe substantially smaller than a width of either the first or secondopening. The initial encapsulation wafer can be etched to form theencapsulation layer with the first cavity, second cavity, and channelbeing associated with the first opening, second opening, and thirdopening, respectively. Those of ordinary skills in the art willrecognize other variations, modifications, and alternatives.

Many benefits are achieved by way of embodiments the present inventionover conventional techniques. For example, embodiments of the presenttechnique provide an easy to use process to integrate a multipledifferent MEMS devices on a single die. In some embodiments, the methodprovides higher device yields in dies per wafer with the integratedapproach. Additionally, the method provides a process and system thatare compatible with conventional semiconductor and MEMS processtechnologies without substantial modifications to conventional equipmentand processes. Preferably, the invention provides for an improvedmulti-MEMS systems and related applications for a variety of uses.Depending upon the embodiment, one or more of these benefits may beachieved. These and other benefits will be described in more throughoutthe present specification and more particularly below.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and accompanying drawings that follow.

FIG. 1 illustrates a simplified cross-sectional diagram 100 of a methodstep of providing a semiconductor substrate with MEMS devices accordingto an embodiment of the present invention. As shown, the present methodcan include providing a semiconductor wafer 110 having multiple MEMSdevices 140 and their electrical interconnects fabricated thereon usingconventional surface or bulk micromachining process. Various componentsare shown, such as bond pads 121, anchors 131, via structures 122, anddielectric and interconnect layers 130, 120. In an embodiment, themultiple MEMS devices 140 can include a first and second MEMS device141, 142. In a specific embodiment, the MEMS devices can be fabricatedon a 10 micron thick silicon layer. The wafer may include materials suchas quartz, silicon carbide, germanium, gallium arsenide, and the like.

FIGS. 2A and 2B illustrate simplified diagrams 200 of a method step ofproviding an encapsulation wafer with cavities according to anembodiment of the present invention. A top view is shown in FIG. 2A anda cross-sectional view, based on a cut along plane 201 in FIG. 2A, isshown in FIG. 2B. In an embodiment, an encapsulation wafer 260 with oneor more cavities can be provided 263. The one or more cavities caninclude a first and second cavity (261, 262), wherein the second cavity262 includes at least one channel 251. A bonding layer 250 can bedeposited for the wafer bonding process. Trenches or cavities withvarying depths can be created by the combination of wet and dry etchingprocesses. In a specific embodiment, the trenches can be fabricated withone etching process by using different etching rates in differentetching areas. For example, the etching rate of deep reactive ionetching is slow at narrow regions. Therefore, one etching process cancreate trenches with varying depths by controlling the areas of theetching regions.

In various embodiments, deep etching loading effect creates a ventinghole wherein the hole can be much shorter than the cavity so that thepackage can be easily sealed hermetically. Sealing processes can includefilm depositions of materials such as oxides, polysilicon, and the like.The advantage of this process is that no extra etching or drilling stepis required to create a much shorter venting hole than the cavity,wherein the cavity is etched using the same deep etching process. In oneembodiment, a feature size of the venting hole or channel is muchsmaller than the cavity. Accordingly, the deep etching process will etchthe venting hole at a different rate with a different feature sizecompared to the cavity. Hence, this phenomenon is described herein as aloading effect of deep etching.

FIG. 3 illustrates a simplified cross-sectional diagram 300 of a methodstep of encapsulating the MEMS devices within cavities according to anembodiment of the present invention. In an embodiment, the device showncan be the bonding of the wafer shown in FIG. 1 and the wafer shown inFIGS. 2A & 2B. FIG. 3 shows the bonding of the silicon wafer 110 withthe MEMS devices 141, 142 and the cap wafer 260. The bonding methods caninclude fusion bonding, anodic bonding, metal layer bonding, eutecticbonding, thermo-compression bonding, glass frit bonding, and the like.The gas and pressure inside the MEMS cavity is determined by the processconditions of the bonding process. In an embodiment, the first andsecond MEMS 141, 142 can be encapsulated within the first and secondcavities (261, 262), respectively. The first MEMS device 141 in thefirst cavity 261 would be encapsulated within a first encapsulationenvironment at a first air pressure.

FIG. 4 illustrates a simplified cross-sectional diagram 400 of a methodstep of etching the cap wafer to vent a cavity according to anembodiment of the present invention. As shown, the cap wafer is etchedfrom the top using any etching or grinding methods. In an embodiment,the cap wafer etching can be applied to the device shown previously inFIG. 3. While cavity A (261) maintains the sealing pressure of theprevious wafer bonding process, the cavity B (262) is vented and hasatmospheric pressure. In an embodiment, the second MEMS device 142within the second cavity 262 can be subjected to a second encapsulationenvironment at a second air pressure via the channel or vent hole. Inthis case, the second air pressure is atmospheric pressure.

FIG. 5 illustrates a simplified cross-sectional diagram 500 of a methodstep of depositing a thin film to seal a cavity according to anembodiment of the present invention. As shown, a thin film 570 isdeposited on the bonded wafer using CVD, PCD, sputtering, evaporation,and the like. The thickness of the thin film 570 needs to be thickenough to seal the vent hole, or channel. The gas and pressure of cavityB is determined by the process pressure during the thin film deposition.In an embodiment, channel of the second cavity can be sealed toencapsulate the second MEMS device within the second cavity at thesecond air pressure.

FIG. 6 illustrates a simplified cross-sectional diagram 600 of a methodstep of opening bond pads according to an embodiment of the presentinvention. In an embodiment, this method can be applied to the deviceshown in FIG. 5. If necessary, the thin film 570 can be partially etchedto open bond pads for assembly processes, such as wafer-level chipprobing or wire bonding.

In an embodiment, the present invention provides a method forfabricating a multiple MEMS device. This method can include a variety ofsteps, which can include those steps described in FIGS. 1-6. The methodcan include providing a semiconductor substrate having a first andsecond MEMS device and providing an encapsulation wafer comprising afirst and second cavity, wherein the second cavity comprises at leastone channel. The first and/or second MEMS device can be selected from amagnetometer, a gyroscope, an accelerometer, an oscillator, a filter, aninfrared sensor, or the like.

The method can include providing a first encapsulation environment at afirst air pressure, and encapsulating the first MEMS device within thefirst cavity and the second MEMS device within the second cavity, whilewithin the first encapsulation environment, to encapsulate the firstMEMS device within the first cavity at the first air pressure. In aspecific embodiment, the first air pressure is below atmospheric airpressure, or in the case the first MEMS is an accelerometer, the firstair pressure is above atmospheric pressure. The first air pressure canbe below the second air pressure. The first encapsulation environmentcan include a gas selected from helium, xenon, krypton, argon, or thelike.

Also, the method can include providing a second encapsulatingenvironment at a second air pressure, wherein the second air pressure isdifferent from the first air pressure, and subjecting the second MEMSdevice within the second cavity to the second encapsulation environmentvia the at least one channel.

The at least one channel can be sealed, while within the secondencapsulation environment, to encapsulate the second MEMS device withinthe second cavity at the second air pressure. The sealing can includedepositing a later of material using a process selected from CVD(Chemical Vapor Deposition), PVD (Plasma Vapor Deposition), sputtering,evaporation, or the like. Furthermore, one or more bond pads can beopened to be exposed through the sealing material.

In a specific embodiment, the method can further include providing aninitial encapsulation wafer, patterning a masking layer on top of thiswafer, and etching this wafer to form the encapsulation wafer. Themasking layer can include a first, second, and third opening, wherein awidth of the third opening is substantially smaller than a width of thefirst opening or the second opening. The etching can be done such thatthe first cavity is associated with the first opening, the second cavityis associated with the second opening, and the third opening isassociated with the at least one channel.

In a specific embodiment, the depth of the at least one channel is lessthan a depth of the first cavity and a depth of the second cavity. Theat least one channel can be provided within the device layer, thedielectric layer, or the interconnect layer. Examples of theseembodiments are also shown in the following FIGS. 7-13. Those ofordinary skill in the art will recognize other variations,modifications, and alternatives.

FIGS. 7-11 illustrates simplified cross-sectional diagrams of a methodstep wherein the wafer cap is bonded to the device layer and the venthole is created on the cap wafer according to another embodiment of thepresent invention. Diagram 700 shows a device similar to that shown indiagram 100 of FIG. 1, but having additional support structures in theMEMS layer. Top and cross-sectional diagrams 800 of FIGS. 8A and 8B showa substantially similar cap structure as in diagram 200 of FIGS. 2A and2B. Diagram 900 of FIG. 9 shows the bonding of the cap wafer shown indiagram 800 to the device wafer shown in diagram 700. Furthermore,diagrams 1000 and 1100 of FIGS. 10 and 11 show the thinning of the capwafer and the deposition of a thin film, respectively. These steps aresimilar to those shown in FIGS. 4 and 5 described previously. Variousmethods of forming a vent hole or channel are shown according toembodiments of the present invention.

FIG. 12 illustrates a simplified cross-sectional diagram 1200 of amethod step wherein the vent hole is created on the device layeraccording to an embodiment of the present invention. Here, the vent holeis etched from a support structure in the MEMS layer, shown by theportion removed within a vicinity of the vent hole area shown in diagram1000 of FIG. 10. As described in previous embodiments, the vent hole orchannel will be sealed by thin film deposition or the like. The positionof the vent hole within the device layer is also shown in a top view1201 of the device.

FIG. 13 illustrates a simplified cross-sectional diagram 1300 of amethod step wherein the vent hold is created in the dielectric orinterconnect layer. Here, the vent hole path is etched through thedielectric or interconnect layer, shown by the path underlying the MEMSlayer within a vicinity of where the vent hole was configured in diagram1000 of FIG. 10. Again, the vent hole will be sealed by thin filmdeposition or the like. The position of the vent hole within theinterconnect or dielectric layer is also shown in a top view 1301 of thedevice.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

What is claimed is:
 1. A semiconductor device having multiple MEMS(micro-electro mechanical system) devices, comprising: a semiconductorsubstrate having a first MEMS device and a second MEMS device; anencapsulation substrate having a top portion and sidewalls forming afirst cavity and a second cavity, the encapsulation substrate beingbonded to the semiconductor substrate with a bonding material at a lowerend of the sidewalls to encapsulate the first MEMS device in the firstcavity and to encapsulate the second MEMS device in the second cavity;wherein the second cavity includes at least one access channel at arecessed region below a first sidewall of the encapsulation substrateadjacent to an interface between the encapsulation substrate and thesemiconductor substrate, the access channel being disposed below abottom portion of the first sidewall without the bonding material; and athin film covering the access channel to seal the second cavity; whereinthe first cavity is at a first atmospheric pressure and the secondcavity is at a second atmospheric pressure, wherein the secondatmospheric pressure is different from the first air pressure.
 2. Thedevice of claim 1 wherein the first sidewall of the encapsulationsubstrate is shorter than the other sidewalls to form the recessedregion below the first sidewall of the encapsulation substrate adjacentto an interface between the encapsulation substrate and thesemiconductor substrate.
 3. The device of claim 2 wherein the first airpressure is below atmospheric air pressure.
 4. The device of claim 1wherein the first MEMS device an accelerometer.
 5. The device of claim 4wherein the first air pressure is above atmospheric air pressure.
 6. Thedevice of claim 1 the first air pressure is below the second airpressure.
 7. The device of claim 1 wherein the first cavity comprises agas selected from a group consisting of: helium, xenon, krypton, andargon.
 8. The device of claim 1 wherein the thin film sealing the atleast one access channel comprises a layer of material deposited using aprocess selected from a group consisting of: CVD, PVD, sputtering, andevaporation.
 9. The device of claim 1 where in the thin film overliesthe encapsulation substrate.
 10. The device of claim 9 wherein the depthof the at least one channel is less than a depth of the first cavity andless than a depth of the second cavity.
 11. A semiconductor devicehaving multiple MEMS (micro-electro mechanical system) devices,comprising: a semiconductor substrate having a MEMS layer that includesa first MEMS device, a second MEMS device, and a MEMS support structure;an encapsulation substrate having a top portion and sidewalls forming afirst cavity and a second cavity, the encapsulation substrate beingbonded to the semiconductor substrate at the sidewalls to encapsulatethe first MEMS device in the first cavity and to encapsulate the secondMEMS device in the second cavity, wherein the second cavity includes atleast one access channel at a recessed region in the MEMS supportstructure adjacent to an interface between the encapsulation substrateand the semiconductor substrate; a thin film covering the access channelto seal the second cavity; wherein the first cavity is at a firstatmospheric pressure and the second cavity is at a second atmosphericpressure, wherein the second air pressure is different from the firstair pressure.
 12. The device of claim 11 further comprising one or morebond pads on the semiconductor substrate.
 13. The device of claim 11wherein the first air pressure is below atmospheric air pressure andwherein the first MEMS device is selected from a group consisting of: amagnetometer, a gyroscope, an oscillator, a filter, and an infraredsensor.
 14. The device of claim 11 wherein the first air pressure isabove atmospheric air pressure and wherein the first MEMS device is anaccelerometer.
 15. The device of claim 11 wherein the encapsulationsubstrate is bonded at the sidewalls to the MEMS support structure inthe semiconductor substrate.
 16. The device of claim 11 wherein the atleast one access channel is located at a recessed region in the MEMSsupport structure.
 17. The device of claim 11 wherein the at least oneaccess channel is located at a recessed region within a device layer inthe semiconductor substrate.
 18. The device of claim 11 wherein the atleast one access channel is located at a recessed region within aninterconnect layer in the semiconductor substrate.
 19. The device ofclaim 11 wherein the at least one access channel is located at arecessed region within a dielectric layer in the semiconductorsubstrate.
 20. The device of claim 16 wherein the first air pressure isabove atmospheric air pressure, and wherein the first MEMS device is anaccelerometer.